I have a 1968 chevy 327 with camel hump heads. I put a hei distributor in it and am wondering what gap to put on the spark plugs? I had a 1980 Malibu years ago and the gap was bigger than my cars with points distributors. I'm running AC delco R45S plugs. The car runs fine but am just wondering if my gap at .035 is too small.
I've been gapping SBC's at .035 for 40 years. It's Sunday, so some folks will chime in with their opinions on this hot, confusing topic.
You can stretch the gap out a little bit with the HEI as they'll fire a plug all the way out to .060 quite reliably, but there's no reason to go that far. Why not set them at .040, drive it for a while and see how it runs, starts, idles, etc. Then when you have an hour to waste stretch the gap out to .050 and see if anything changes. Or if you're not the type that likes to experiment, leave 'em at .035 and don't worry about it.
I run an HEI. It's been hopped up a bunch. It's unbelievable what you can do with one. I know the air to fuel ratio I'd some where around 13 to 1 but gasoline is power and if you can run it richer and fire it clean you will make more HP I guarantee it. The carb I run would be so rich on another engine I'd bet it would not run and my gap is nearing .070" and I'm still jetting up. Anyway if you decide to widen the spark plug gap carry an extra rotor because the extra voltage and power can blow a hole in it but at .035" most likely not.
the wide gaps kill the rotor like jimmy said ( specially if the rotor is a cheap one also had some crossfire in the caps if the terminals were aluminum ) and had a few arc over wires at .060 due to old/poor insulation ( 7mm packards) , I used the revised gap of .045 that chevy used . at .045 you can run a leaner idle mixture .
When HEI first came out the plug gap was .080 to fire the lean fuel mixture to meet the smog law. .040 will work just fine.
yeah, they started with a pretty wide gap, but after a few years they figured out that folks never bothered changing plugs, and the gap would open way up in 50k-100k miles. They eventually settled on .045. That's what I run on a Chevy with an HEI. works fine They are not picky at all, they'll work anywhere from .030 to .080
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